UCDS for Augmentor Damping

ABSTRACT: Combustion instability (aka thermoacoustic instability) is a significant issue in propulsion systems including augmentors. Oscillations can increase heat transfer to walls 10 fold and cause vibration damage to the propulsion system and the surrounding system. This damage can occur very rapidly. Combustion instability (CI) is challenging to design for due to the complex interactions between the unsteady flow-field and combustion, as a result most systems are not able to be designed for stability. Instead, best practices and experience are used to minimize the risk, and when CI occurs in testing changes are attempted to fix the problem. These changes include damping systems such as liners and absorbers. In this effort GTL proposes to demonstrate the ability to design damping systems by understanding the system instability. Here GTL will model the AFRL flameholder in order to determine the magnitude of the instability sources. This then quantifies how much damping energy is required. Damping methods can be modeled and judged against this criteria. From this recommendations for damping methods will be put forward. This methodology can then be applied to augmentor systems in order to provide a damping method that is capable of performing at full scale. This will avoid issues where laboratory experiments do not scale. GTLs analysis method is also capable of identifying the sources of instability providing avenues for avoiding instability as opposed to damping. GTL has used its methods to model instabilities in scramjets, the J85 augmentor and many rocket systems. Validating GTLs methods leads to the more ideal design-for-stability process. Funding this effort would get us closer to that reality in augmentors. BENEFIT: Understanding combustion instability (CI) (aka thermoacoustic instability) would be a great benefit to propulsion system designers of all types. CI is a major technical risk in any new system development program. This effort acts to improve our understanding of damping systems and how they can be applied. In addition, this understanding also acts to uncover the causes of instability leading to methods that avoid the source of instability as opposed to damping it after the fact. GTL has used its models to analyze scramjets, augmentors and many rocket systems and seeks to further improve its ability to model augmentor instabilities and damping methods. Eliminating instability as a design concern will significantly decrease development cost and risk. This will in turn allow engineers to produce more innovative designs without risk of instability. More efficient, lower cost, higher performing engines will be the result.